Essentially, supply and demand meet each other, but that doesn't explain prices alone, why a chair sells for 100 USD while a car sells for 50,000 USD. What matters is the difference in resources needed to devote to create one, ie labor time and raw materials, as well as the extent to which machinery, ancillary materials, semi-finished goods, etc are used up.

For a car, you use up far more of these than for a chair. A sudden influx of cars, say, by discovering a hidden trove, or a sudden decrease, ie a warehouse exploded, will have temporary distortions on price. However, this central, "natural price" is what supply and demand press towards over time.

Further, since raw materials exist naturally, the difference in their value is driven by the labor required to extract them, refine them, etc. Each step in the process makes it more valuable, unless supply is kept artificially low or high. Further still, these are averages. If someone spends a lot of time making an equivalent chair, they aren't going to be able to take it to market for a higher price.